There is a heightened concern over underwater attacks on ships in port and the port facilities. Some of the underwater threats of greatest concern are presented by swimmers/divers or small unmanned systems that can enter a port's waters undetected relatively easily. Currently, a variety of sensor, physical barrier, and response systems are available to prevent such underwater invasions. Although effective systems have been demonstrated, they are not suitable for widespread civilian and commercial in-port use due to safety and/or environmental issues, or they are cost prohibitive to deploy in large numbers.